The present disclosure relates to an image forming apparatus of a copy machine, a printer, a facsimile, and a multi-function machine of them that use an electro-photographic system, more particularly, to an image forming apparatus that supplies a developer from a developer supply device to a development device.
In an image forming apparatus that uses a two-component developer which contains toners and magnetic carriers, a toner concentration in a development device is detected by means of a toner concentration sensor, and if the toner concentration becomes low, toners are supplied from a developer supply device such as a toner container and the like to the development device. By stirring the developer in the development device and the supplied toners by means of a stir member, a change in the toner concentration in the development device is made small.
When toners are supplied from the developer supply device to the development device via a supply opening and the supplied toners are stirred and conveyed in a convey route in the development device, as the convey distance from the supply opening becomes long, the stir time of the developer increases, accordingly, the change amplitude of the toner concentration becomes small. However, the change amplitude of the toner concentration becomes large near the supply opening, accordingly, there is a problem that unevenness of the toner concentration in the convey direction occurs.
Here, an image forming apparatus is known, which alleviates the unevenness of the toner concentration in the development device. In the image forming apparatus, the development device is provided with two supply openings through predetermined positions in the convey direction of the developer, toners are supplied from the two supply openings at the same time, whereby the change in the toner concentration in the convey direction is alleviated.
In the above image forming apparatus, the toner concentration is detected by means of the toner concentration sensor, and as a result of this, when it is found out that the toner concentration becomes low, toners are supplied from the toner container to the development device. Besides, immediately before toners are supplied, various images are printed. For example, in a case where images having a low coverage rate are sequentially printed and the toner concentration becomes low, because of the sequential printing, the developer is repeatedly stirred. There is a risk that the toners in the development device could be brought to an excessively electrified state thanks to the long-time stirring. When the toners in the development device is in the excessively electrified state and new toners are supplied from the toner container, the supplied toners are supplied to a development roller with being kept at a low electrification. Besides, in a case where printing of many paper sheets is executed immediately before replacement of the toner container, because of the printing of many paper sheets, the developer in the development device is repeatedly stirred. There is a risk that the toners in the development device could be brought to an excessively electrified state thanks to the long-time stirring. When the toners in the development device is in the excessively electrified state and fresh toners are supplied from the toner container, the supplied toners are supplied to the development roller with being kept at a low electrification. There is problem that when an electrostatic latent image on a photoreceptor is developed by using the low-electrification toners, image defects such as image fogging and the like occur.
The present disclosure provides an image forming apparatus that alleviates unevenness of the electrification amount of a developer in a development device in a case where the developer is supplied from a replacing developer supply device to the development device or in a case where the remaining amount of the developer becomes less and a developer is supplied to the development device.